Thermoplastic polyester resin compositions have found wide commercial acceptance because they can be formed into strong abrasion-resistant fibers, films and molded articles. Those skilled in the art have endeavored to develop new types of polyester resins which have improved tensile strength, stiffness, elongation, impact strength, flame resistance, thermal and chemical resistance, and the like. Wholly aromatic polyester resins exhibit improved thermal and chemical stability, but they have exceedingly high melt viscosities and require high processing and fabrication temperatures for injection moldings or melt extrusion into films, fibers or other shaped articles.
Polyester resin compositions tend to be highly susceptible to hydrolytic conditions and corrosive environments. The carbonyloxy moieties in polyester resin compositions are highly reactive and readily enter into chemical transformations. For example, in the production of segmented polyester resins, it is a disadvantage that transesterification occurs between prepolymer reactants, and the resultant polyester resin has a random configuration rather than the desired segmented copolymer structure.
Accordingly, it is an object of the present invention to provide polyester resin compositions which have improved thermal and chemical stability.
It is another object of this invention to provide high molecular weight polyester resin compositions which are soluble in solvents and can be conveniently converted into films and molded articles.
It is another object of this invention to provide polyester resins which are hydrolytically stable and adapted for injection moldings or melt extrusion into flame resistant fibers and other shaped articles.
It is a further object of the present invention to provide a method for producing segmented polyester resin copolymers wherein random transesterifications between prepolymer reactants is suppressed.
Other objects and advantages shall become apparent from the following description and examples.